Population genetics ofDrosophila ananassae

Abstract

SummaryDrosophila ananassaeDoleschall is a cosmopolitan and domestic species. It occupies a unique status amongDrosophilaspecies due to certain peculiarities in its genetic behaviour and is of common occurrence in India. Quantitative genetics of sexual and non-sexual traits provided evidence for genetic control of these traits.D. ananassaeexhibits high level of chromosomal polymorphism in its natural populations. Indian natural populations ofD. ananassaeshow geographic differentiation of inversion polymorphism due to their adaptation to varying environments and natural selection operates to maintain three cosmopolitan inversions. Populations do not show divergence on temporal scale, an evidence for rigid polymorphism.D. ananassaepopulations show substantial degree of sub-structuring and exist as semi-isolated populations. Gene flow is low despite co-transportation with human goods. There is persistence of cosmopolitan inversions when populations are transferred to laboratory conditions, which suggests that heterotic buffering is associated with these inversions inD. ananassae. Populations collected from similar environmental conditions that initially show high degree of genetic similarity have diverged to different degrees in laboratory environment. This randomness could be due to genetic drift. Interracial hybridization does not lead to breakdown of heterosis associated with cosmopolitan inversions, which shows that there is lack of genetic co-adaptation inD. ananassae. Linkage disequilibrium between independent inversions in laboratory populations has often been observed, which is likely to be due to suppression of crossing-over and random genetic drift. No evidence for chromosomal interactions has been found in natural and laboratory populations ofD. ananassae. This strengthens the previous suggestion that there is lack of genetic co-adaptation inD. ananassae.